With the recent development of information communication technology, a variety of wireless communication techniques are being developed. From among them, a WLAN is technology for wirelessly accessing the Internet at homes or companies or in specific service providing areas using mobile terminals, such as a Personal Digital Assistant (PDA), a laptop computer, and a Portable Multimedia Player (PMP), based on radio frequency technology.
Lots of standardization tasks are being carried out since and Electronics Engineers (IEEE) 802 (i.e., a standard organization for WLAN technology) was set up on February, 1980. Initial WLAN technology was able to support the rate of 1 to 2 Mbps through frequency hopping, band spreading, and infrared communication by using a 2.4 GHz frequency in accordance with the IEEE 802.11 standard, but the recent WLAN technology can support a maximum rate of 54 Mbps by using Orthogonal Frequency Division Multiplexing (OFDM). Furthermore, in IEEE 802.11, the standards of various technologies, such as the improvements of Quality of Service (QoS), the compatibility of Access Point (AP) protocols, security enhancement, radio resource measurement, a wireless access vehicular environment, fast roaming, a mesh network, interworking with an external network, and wireless network management, are put to practical use or being developed.
IEEE 802.11b of the IEEE 802.11 supports a maximum transmission speed of 11Mbs while using the 2.4 GHz frequency band. IEEE 802.11a commercialized after IEEE 802.11b has reduced the influence of interference as compared with the very complicated 2.4 GHz frequency band by using a 5 GHz frequency band not the 2.4 GHz frequency band and also has improved the communication speed up to a maximum of 54 Mbps using OFDM technology. IEEE 802.11a, however, is disadvantageous in that the communication distance is shorter than that of IEEE 802.11b. Furthermore, IEEE 802.11g, like the IEEE 802.11b, implements a maximum communication speed of 54 Mbps using the 2.4 GHz frequency band and satisfies backward compatibility. Thus, IEEE 802.11g is significantly being in the spotlight and is superior to IEEE 802.11a even in the communication distance.
Furthermore, in order to overcome limitations to the communication speed that has been considered to be weakness in a WLAN, an IEEE 802.11n standard has recently been established as a technology standard. An object of the IEEE 802.11n standard is to increase the speed and reliability of a network and to expand the coverage of a wireless network. More particularly, in order to support a High Throughput (HT) having a maximum data processing speed of 540 Mbps or higher, minimize a transmission error, and optimize the data rate, the IEEE 802.11n standard is based on Multiple Inputs and Multiple Outputs (MIMO) technology using multiple antennas on both sides of a transmitter and a receiver. Furthermore, the HT WLAN system may use a coding scheme for transmitting several redundant copies in order to increase reliability of transmission data and may use Orthogonal Frequency Division multiplexing (OFDM).
As a WLAN is actively propagated and applications employing the WLAN are diversified, there is recently a need for a new WLAN system for supporting a throughput higher than the data processing speed supported by an HT WLAN system. A Very High Throughput (VHT) WLAN system is one of IEEE 802.11n WLAN systems which have recently been proposed in order to support a data processing speed of 1 Gbps or higher.
In IEEE 802.11 TGac in which the standardization of a VHT WLAN system is in progress, active research is being done on a scheme using 8×8 MIMO and a channel bandwidth of 80 MHz or higher in order to provide a throughput of 1 Gbps or higher.
The VHT WLAN system can support Multiple Input Multiple Output (MIMO) technology which is capable of transmitting data to a single user or multiple users at the same time by using a plurality of spatial streams.
When data is transmitted using a plurality of spatial streams, the spatial streams may experience different channel environments. Accordingly, a channel may need to be estimated for every spatial stream and a Modulation and Coding Scheme (MCS) to be used may need to be set.
In order to determine an MCS value to be applied to data that will be transmitted by an STA, an STA that will receive data may be requested to make feedback by deriving an MCS value. An STA requesting an MCS FeedBack (MFB) may be referred to as an MFB requester, and an STA sending the MFB in response to the MFB request may be referred to as an MFB responder. A procedure of the MFB requester receiving the MFB from the MFB responder through the MFB request is called a link adaptation procedure.
It is preferred that, when the MFB responder sends the MFB by deriving the MCS value in response to the MFB request, information (i.e., a basis to derive the MCS value) be determined by taking various factors that may have an effect on the transmission of data through subsequent actual spatial streams into account. In a VHT WLAN system using various coding schemes, various channel bandwidths, and a plurality of spatial streams, the factors may be further increased. However, to provide an MFB responder with information so that various factors may be all taken into account may be impossible or may be limited in terms of backward compatibility.
Accordingly, a method of an MFB responder feeding back a recommended MCS value, obtained by adaptively deriving an MCS, in response to MFB requests of various methods and a method of providing information so that an MFB responder can derive an optimum recommended MCS value need to be taken into consideration.